Cholinergic neurotransmission has unique relevance for mental health. Acetylcholine (ACh) plays a key role in generating the rapid eye movement (REM) phase of sleep, and REM sleep abnormalities typify some forms of depression. ACh is important for generating the cortical activation needed for attentional, learning, and memory functions of normal wakefulness, and schizophrenia and bipolar disorder are characterized by alterations in cortical activity and by sleep disruption. The health relatedness of this research program is clear from the facts that: 1) sleep disruption is a feature of all psychiatric diseases;2) some clinical traits of depression are caused by altered cholinergic neurotransmission;and 3) altered cholinergic transmission contributes to the cognitive deficits of schizophrenia. Relevance to public health is evidenced by World Health Organization data reporting that 450 million people worldwide suffer from some form of mental or brain disorder, and that in the West mental disorders account for 80% of premature deaths in young adults. The long-term objectives of this research program are to identify modulators of cholinergic neurotransmission in brain regions that regulate sleep and wakefulness. Methods include: 1) in vivo microdialysis and microinjection for drug delivery to selective brain regions and for collecting endogenously released neurotransmitters;2) high performance liquid chromatography and capillary electrophoresis to measure changes in endogenous neurotransmitters caused by antipsychotic drugs;and 3) polygraphic recordings of the cortical electroencephalogram to quantify sleep and wakefulness. These techniques will be used to achieve four specific aims relevant for the NIMH mission to reduce the burden of mental illness through brain research. Specifically, the aims were developed in recognition of the NIMH Director's statement acknowledging the need for translational research contributing to the development of new medications that will more effectively treat people suffering from schizophrenia, depression, and bipolar disorder (http://www.nimh.nih.gov/about/director/testimonv/2007-senate-appropriations.cfm ). Aim 1 will test the hypothesis that atypical antipsychotics, such as olanzapine, alter cholinergic transmission in the prefrontal cortex. Aim 2 will test the hypothesis that the increase in wakefulness caused by hypocretin (orexin) is mediated, in part, by GABAergic transmission in the pontine reticular formation. Aim 3 will test the hypothesis that GABAergic and cholinergic transmission in the pontine reticular formation interact to regulate levels of arousal. Aim 4 will test the hypothesis that GABA and glutamate levels in the pontine reticular formation change in a reciprocal fashion during sleep and wakefulness. The aims are unified by their ability to provide insights into the neurochemical mechanisms modulating cholinergic neurotransmission in brain regions regulating sleep and wakefulness.